Failure Analysis of Oil and Gas Production Tubing in an Inclined Well

摘要

Based on various laboratory investigations and analytical studies, it was concluded that localized pitting corrosion occurred because of the presence of corrosive agents (CO_2, H_2S, and salt) dissolved in produced water. Corrosion was further aggravated by material imperfections coupled with aging, which rendered the material weak and vulnerable and caused multiple holes and the formation of a slit/rupture in the tubing. Cracks originated from corrosion pits and inclusions and propagated under stresses as corrosion fatigue cracks. Once a crack started, propagation of the crack led to an overload failure in which the remaining intact metal ligament was no longer large enough to support the applied tensile stresses. Use of L-80 Type-I CS tubing in place of N-80 is recommended per literature for the field conditions under discussion.